The use of immobilized lipase preparations for the transesterification of fats is well known. For example, in UK Patent 1,577,933, an immobilized lipase suitable for transesterification is attached on an indifferent particulate carrier which may be diatomaceous earth or alumina and which exhibits a very high surface area. It has also been proposed to prepare an immobilized lipase preparation for interesterification with n-hexane as a solvent comprising lipase and a strong anion exchange resin (see European Journal of Applied Microbiology and Biotechnology, no. 14, p. 1-5 (1982)). E.P.O. application No. 0069599 discloses a lipase enzyme suported on a carrier such as Celite.RTM. for continuous interesterification in a column.
In Biotechnology and Bioengineering, vol. XV, p. 359-375, 1973, G. Broun et al, methods of cross-linking enzyme molecules inside a matrix with or without an inactive protein are described. More specifically, the method comprises the cross-linking of an enzyme molecule with an inactive protein, such as albumin, in the presence of a bifunctional cross-linking agent without any preformed matrix.
In practice, this article teaches the mixing of albumin, glutaraldehyde and an enzyme in a phosphate buffer, freezing the solution obtained at -30.degree. C. and allowing the frozen mass to warm at 4.degree. C. After standing for 4 hours at 4.degree. C., the spongelike proteinic copolymer is thoroughly rinsed, lyophilized and ground. It is then suitable for suspending in a mixed solution of substrate or for pouring into a column with a flux of substrate solution flowing through it. Examples using glucose oxidase, urease, trypsin and catalase are given.
Unfortunately, it has been found that when any of the enzymes used in the G. Broun et al disclosure is replaced by lipase, there is no obtention of a solid matrix. It is however possible to obtain the desired porous matrix by increasing the amount of bifunctional cross-linking agent but in this situation, the lipase enzyme loses its activity after lyophilization.
Therefore, a method making the use of active immobilized lipase possible would be highly desirable.